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[en] Various solution-treatments were applied on a rapidly solidified and subsequently rolled Mg-7.50Al-1.07Ca-0.17Mn (mass%) alloy sheet, and a room-temperature stretch formability, tensile properties, microstructures, and textures of the solution-treated sheets have been investigated. Although the solution-treatment at 400 °C gives high strengths, the sheet shows poor room-temperature stretch formability with the Index Erichsen value of 4.8 mm due to densely dispersed second phase particles. Also, the particles tend to distribute to the rolling direction, leading to limited elongation to failure of 11.0% along the transverse direction. The solution-treatment at higher temperature leads to the sparse and relatively uniform dispersion of the particles. This results in the significant improvement in the room-temperature stretch formability and ductility. The Index Erichsen increases to 6.8 mm by the solution-treatment at 450 °C for 4 h, and the sheet shows large elongation to failure of 19.1% and 17.1% along the rolling and transverse directions, respectively. The sheet also exhibits high strengths and in-plane isotropic properties, tensile strength over 320 MPa and 0.2% proof stress of ~180 MPa could be obtained due to fine grain structure with the average grain size of 9.5 μm.
[en] Refining the grain size of γ-TiAl alloys to improve their strength and ductility is of academic interest. Thus, we report a multi-stage heat treatment method consisting of solution treatment, cyclic heat treatment, annealing, short heat treatment, and aging to refine the microstructure of the Ti–48Al–2Cr–2Nb alloy. The solution-treated microstructure was refined from 1100 to 191 μm by cyclic heat treatment, promoting feathery γ packets. Fine duplex grains below 23 μm were obtained through discontinuous coarsening, which was accelerated in the cyclic-heat-treated alloys owing to the high driving force resulting from the presence of feathery γ packets and fine interlamellar spacing. Through the short heat treatment and aging at single α and α2 + γ fields, a tailored duplex structure with a grain size of 24 μm and interlamellar spacing of 42 nm was achieved. Through microstructure refinement, tensile strength and elongation were improved to 697 MPa and 2.1%, respectively, compared to those of the conventional forged specimen (622 MPa and 1.3%, respectively). We believe that our study provides a simple pathway to refine the grain size and interlamellar spacing of γ-TiAl alloys.
[en] In the research project 'Determination of steel structures by means of ultrasound' methods are developed for the non-destructive structure characterization with scattered ultrasound. Measurements were made at about 200 steel samples with frequencies between 5 and 20 Mc/sec. In the range of 0,05 <= d/lambda <= 0,5 (d=mean grain size, lambda = wavelength of the ultrasound pulse) known theories can be applied for the quantitative grain size determination and with an accuracy of +-15% the results agree with the metallographically measured values. The best method for this is the combination of two measurements with two different frequencies. Advantages are given by the measurement of the multiple scattering which is leading to the scattering coefficient and to the grain size with one measurement only and without assumptions concerning other parameters of ultrasound propagation. A structure characterization concerning the homogeneity inside the material is possible, too, because of the time (i.e. sound path-)-dependent scattering measurement. It is able to control the structure of monophasic steels with grain sizes between ASTM 1 and ASTM 11. Today problems unsolved are the martensitic steels, the multiphasic structures
[en] In this work, we explore the influence of the grain size distribution (GSD) on density, connectivity and internal forces distributions, for both 2D and 3D granular packings built mechanically. For power law GSDs, we show that there is an exponent for which density and connectivity are optimized, and this exponent is close to those that characterize other well known GSDs such as the Fuller and Thompson distribution and the Appollonian packing. In addition, we studied the distributions of normal forces, finding that these can be well described by a power-law tail, specially for the GSDs with large size span. These results highlight the role of the GSD on internal structure and suggest important consequences on macroscopic properties.
[en] Commercial copper was submitted to a thermomechanical treatment in order to study its influence on the velocity of artificial green patina formation by immersion as well as on the thickness and adherence of the corrosion product formed on the underlying metal. The thermomechanical treatment enabled us to obtain samples with 9 to 60 μm grain size. The samples were submitted to an accelerated attack by immersion in an electrolytic bath in order to obtain a green patina. On the smallest grain size material it can be observed a patina with high thickness and adherence smooth texture and homogeneous morphology. From the electrochemical assays it was established that the passivity current decreases for decreasing grain sizes. These results are consistent with the minimal porosity presented by the patina morphology which increase the protecting power. The underlying material did not present localized attack. (Author) 10 refs
[en] In this work, high temperature solid phase method was applied to prepare Sr2MgSi2O7:Eu, Dy blue light long-persistence materials with different contents of H3BO3. Under the condition of low H3BO3 content, it was difficult for Eu and Dy to enter Sr2MgSi2O7 lattice, impurity phase of Sr3MgSi2O8 was observed, and initial afterglow luminance of the sample was very low. With the increase of H3BO3, Sr3MgSi2O8 phase disappeared, Eu and Dy entered Sr2MgSi2O7 lattice smoothly, and the grain size as well as initial afterglow luminance of samples increased significantly. The initial afterglow luminance of the sample reached the maximum while the H3BO3 content was 10% (molar ratio). As H3BO3 content increased further, the initial afterglow luminance reduced rapidly. After detailed analysis, we consider that the key factors influencing the afterglow luminance of samples are the formation and the density of luminous unit, which is greatly determined by the Eu and Dy’s entering Sr2MgSi2O7 lattice as well as the grain size of Sr2MgSi2O7 crystal. (paper)
[en] The effects of grain sizes and sensitization on the creep behavior of AISI 304 stainless steel was investigated. The study state creep rate of sensitized specimens was always larger than that of non-sensitized ones. The carbides were precipitated on grain boundary during creep and this seemed to have an effect on steady-state creep rate. All of ruptured specimens mainly showed intergranular cracking. (Author)
[en] Microstructure evolution in non-conserved and volume-conserved isotropic two-phase grain structures, with equal interfacial energy for all interfaces and equal volume fractions of the two-phases, is compared based on large-scale phase-field simulations. Two important observations are as follows: (1) the growth mechanism has a larger effect on the grain size distributions of the two alloys than on their grain topology distributions; (2) the growth rate and normalized grain size relation of the grains per topological class are much more scattered for the conserved system than the non-conserved system.